Superstring Theory

The need to develop a quantum theory of gravity has bedeviled theoretical physicists since the 1940's, and one approach after another has met with failure. However, after decades of frustration, many physicists now believe that we are well along the road to a solution, in the form of a quantum theory called superstrings. As its name suggests, the theory conceives of fundamental particles, such as electrons or quarks, not as pointlike objects but rather as tiny strings, with lengths of about 10 to the minus 33nd power centimeter. The particles that transmit forces between particles of matter are also viewed as strings. The theory holds that the force of gravity is conveyed by a looplike particle called a graviton, and all the various kinds of particles exist in a 10-dimensional realm–the 4 dimensions we are familiar with in our everyday world (height, width, depth, and time) and 6 extra dimensions.

Why, then, do we not see these extra dimensions? The answer can be understood by thinking about an ordinary soda straw. By looking closely at the straw, you can see that it is a curved two-dimensional surface. However, if you look from a distance, you cannot see the thickness, and the straw looks like a one-dimensional line. Superstring theory proposes that the 6 extra dimensions are curled in this way, with a circumference of about 10 to the minus 32nd power centimeter. Unfortunately, the mechanism that causes this curling is not well understood.

While superstring theory was invented as a quantum theory of gravity, it appears to be much more far-reaching than anyone had anticipated. If the superstring theory is right, it could very well be the conclusion of our search for the fundamental laws of nature.